1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus for performing a heat treatment on a semiconductor substrate implanted with impurities by light irradiation.
2. Description of the Background Art
Conventionally, a lamp annealer employing a halogen lamp has been typically used in the step of activating impurities in a semiconductor wafer after impurity (ion) implantation. Such a lamp annealer carries out the activation of impurities in the semiconductor wafer by heating (or annealing) the semiconductor wafer up to a temperature of, e.g., about 1000° C. to 1100° C. Such a heat treatment apparatus utilizes the energy of light emitted from the halogen lamp to raise the temperature of the substrate at a rate of about hundreds of degrees per second.
On the other hand, in recent years, with the increasing degree of integration of semiconductor devices, it has been desired to provide a shallower junction as the gate length decreases. It has turned out, however, that even the execution of the process of activating impurities in a semiconductor wafer by the use of the above-mentioned lamp annealer which raises the temperature of the semiconductor wafer at a rate of about hundreds of degrees per second produces a phenomenon in which the impurities of boron, phosphorus and the like implanted in the semiconductor wafer are diffused deeply by heat. The occurrence of such a phenomenon causes the depth of the junction to exceed a required level, giving rise to apprehension about a hindrance to good device formation.
To solve this problem, for example, US 2006/0291835 proposes a technique for irradiating a surface of a semiconductor wafer with flash light by using a xenon flash lamp (hereinafter, even when referred to simply as a “flash lamp”, it refers to a xenon flash lamp) to raise the temperature of only the surface of the semiconductor wafer, which is implanted with impurities, in an extremely short time (several milliseconds or less). The xenon flash lamp has a spectral distribution of radiation ranging from ultraviolet to near-infrared regions. The wavelength of light emitted from the xenon flash lamp is shorter than that of light emitted from the conventional halogen lamp, and almost coincides with a fundamental absorption band of a silicon semiconductor wafer. It is therefore possible to quickly raise the temperature of the semiconductor wafer, with a small amount of light transmitted through the semiconductor wafer, when the semiconductor wafer is irradiated with flash light emitted from the xenon flash lamp. Also, it has turned out that the flash light irradiation in an extremely short time of several milliseconds or less can selectively raise the temperature of only near the surface of the semiconductor wafer. Therefore, the temperature rise in an extremely short time by using the xenon flash lamp allows the execution of only the impurity activation without deep diffusion of the impurities.
After such a process of activating impurities as discussed above, usually, a front surface cleaning process is performed on the semiconductor wafer in order to remove a resist film or the like. For a shallower junction, however, impurities are implanted only into a topmost surface layer of the semiconductor wafer. Therefore, in the front surface cleaning process, the layer implanted with impurities is removed from the semiconductor wafer.
FIG. 11 is a graph showing impurity concentration distributions in the vicinity of a surface of a semiconductor wafer before and after cleaning in the background art. In this figure, the horizontal axis represents the depth from the surface of the semiconductor wafer and the vertical axis represents the impurity concentration. As shown in FIG. 11, a large amount of impurities are removed from the surface layer of the semiconductor wafer by the front surface cleaning process and few impurities remain after cleaning. Thus, there arises a problem that it can not serve as a semiconductor device due to removal of the impurities.